<!doctype html>
<html>
<head>
<style type="text/css">
fieldset {
 margin: 0; padding: 0;
 border: none;
}
#float {
 float: left;
 width: 10em; height: 5em;
 background-color: green;
}
#sibling {
 width: 5em; height: 10em;
 background-color: blue;
}
</style>
</head>
<body>
<fieldset>
 <div id="float"></div>
 <div id="sibling"></div>
</fieldset>
</body>
</html>
